Power domain Non-Orthogonal Multiple Access (PD-NOMA) is an emerging name amongst the candidate technologies which are being considered for the deployment of fifth-generation networks. This medium access technique employs superposition of signals at the transmitter side for transmission and successive interference cancellation to retrieve the separate signals at individual receivers. For maximum utilization of PD-NOMA technique, the optimization of the power allocation coefficient values used for the superposition of the signals is crucial. This paper proposes nature inspired (NI) algorithms viz. Particle Swarm Optimization (PSO), Firefly Algorithm (FA), Differential Evolution (DE), and Simulating Annealing (SA) for finding the optimum value of the power allocation coefficient for two user PD-NOMA. Numerical results show that by calculating power allocation coefficient using NI algorithms, the performance of the PD-NOMA has been enhanced in terms of Probability outage with respect to SINR. Moreover, simulations are performed to calculate power allocation coefficient by varying distance between two receiver nodes. Further, a comparison between different NI algorithms based power allocation coefficient calculations is compiled in terms of computational time and convergence and it is observed that the DE algorithm-based power allocation co-efficient calculations outperforms all other algorithms by 42.65%.